need opinion on replacing the ecu on the S600

Not a good idea..
The guys I talked to about it say they will be almost doing it blind.. not a lot of V12 600 cars have owners who want to do things to them..

If I might just ask you this..
WHY do you need to play with your Benz.. what particular thing is it you are trying to achive.. If you are honest about it we (most of us on here) will be happy to help..
You should be aware however.. just like any thouroughbred, if you mess with it or treat it badly.. it will cost you
BIG TIME

Just get a written guarantee that the chip will give the performance gains

that they say or you get your money back. Protect yourself. Their answer for the chip not doing what they say may be, "Of course because you haven't also done the proper intake, header, and muffler modifications, too." Then, you have to decide how much more money you want to spend before finding out the power gains may only be minimal. Or they may be reasonable, I don't know.

My simple advice is to protect yourself. Get all guarantees in writing. And, be ready to spend more than you expected for real HP gains.

Brett

An easier way would be to add nitros to the intake manifold.. slow bleed or boost and Kick..
Not sure how the driveshaft coupling would hold up if you did though.. and will the box take it?

Personally, messing with "power" chips scares the hell out of me. I would be hard pressed to trust the developers of such an item. I am not convinced that they have taken into account (or even understand) all that goes on in the engine management system.

hmm..if a 600 is not fast enough for you then you need to get a different car.

In the right gear my 600 can pull with any sports car.

i've either owned or driven them all, only a small percentage will walk away from a 600.